VZV is a virus which causes varicella, encephalitis, hepatitis or the like by primary infection, and after entering a latent stage, sometimes relapses as varicella zoster.
It is known that varicella in immunocompromised hosts sometimes becomes fatal to the host, and zoster sometimes causes post herpetic neuralgia after recovery from the disease.
As drugs for these diseases Acyclovir (Wellcome, England), varicella live vaccine (Research Institute for Microbial Diseases Osaka University, Japan), BV-Ara U (Yamasa Shoyu, Japan) and the like are mentioned, but these do not have satisfactory safety and effectiveness, and therefore, the development of drugs which can be prophylactically administered and have high safety and effectiveness, is required.
It was recognized that a human immunoglobulin formulation obtained from human serum after suffering from varicella zoster (Varicella-Zoster Immune Globulin: VZIG; trade name Varitect, etc.) is effective to some extent (Zaia, J. A. et al., J. Infect. Dis. Vol. 147, pp 737-743, 1983), but the neutralization titer of VZIG against VZV is only several or several tens of times that of a conventional human immunoglobulin formulation, and therefore, drugs having a higher neutralization titer are needed. Moreover, a supply of VZIG is difficult, and there are problems of cost and maintaining a constant supply. In addition, human serum is intrinsically accompanied by the risk of contamination with unknown factors such as the AIDS virus or the like. To solve these problems, MAbs to VZV have been developed.
Some groups (Friedrichs, W. E., and Grose, C., J. Virol. Vol. 49, pp 992-996, 1984; Keller, P. M. et al., J. Virol. Vol. 52, pp 293-297, 1984; Forghani, B. et al., J. Virol. Vol. 52, pp 55-62, 1984) prepared mouse monoclonal antibodies (mouse MAb) which specifically bind to VZV or a glycoprotein of 105-118 k Daltons present in a cell infected with VZV and designated as gpIII or gA (hereinafter abbreviated as gpIII; see, Davison, A. J. et al., J. Virol. Vol. 57, pp 1195-1197, 1986).
Where, however, a mouse monoclonal antibody is administered to a human, it is recognized as a heterologous protein, and may cause side effects such as anaphylatic shock. Moreover, the mouse MAb is known to be depleted from the blood rapidly by human antibodies produced in vivo against the mouse MAb. This offsets the advantages of a protein having a low toxicity and high stability.
Therefore, for treatment of VZV infectious diseases, a human-type MAb (HuMAb) is required.
As the HuMAb to VZV, there are known HuMAb (Foung, S. K. et al., J. Infect. Dis. Vol. 152, pp 280-285, 1985) to a glycoprotein of VZV designated as gpII or gB (hereinafter abbreviated as gpII; see, Davison, A. J. et al., J. Virol. Vol. 57, pp 1195-1197, 1986), and HuMAb (see, Sugano, T. et al., Eur. J. Immunol., Vol. 17, pp 359-364 and Japanese Unexamined Patent Publication No. 62-42933, and EP No. 0198086 and U.S. Pat. No. 4,950,594) to a glycoprotein of VZV designated as gpI or gC (hereinafter abbreviated as gpI; see, Davison, A. J. et al., J. Virol., Vol. 57, pp 1195-1197, 1986).
The neutralizing activity of HuMAb to gpI, however, is dependent on complement, and therefore, the neutralizing activity is remarkably reduced when complement is not added. Moreover, although HuMAb to gpII does not need the addition of complement for neutralizing activity, its neutralization titer (in terms of the amount of antibody which neutralizes 50% of the virus) is lower than that of HuMAb to gpI in the presence of complement.
Studies have been made using mouse MAb, to determine which antigen of VZV is most suitable for prevention of an infection by VZV. According to Keller et al. (Keller, P. M. et al., J. Virol., Vol. 52, pp 293-297, 1984), although antibody to gpIII exhibited a high neutralizing activity regardless of the presence or absence of complement, antibody to the gpI neutralized virus only with the addition of complement and many of the antibodies to gpII did not neutralize the virus, regardless of the presence or absence of complement. Similar results were revealed by Grose, C. H. et al. (Grose, C. H. et al., Inf. Immun., Vol. 40, pp 381-388, 1983) and Forghani B. et al. (Forghani B. et al., J. Virol., Vol. 52, pp 55-62, 1984). Moreover, it is known that an MAb to gpIII of VZV inhibits the spread of VZV from an infected cell to a noninfected cell (intercellular infection-inhibiting activity or virus spread-inhibiting activity). This activity was not found for MAb's to the gpI or gpII.
It has been revealed that antibody to gpIII is important for prophylaxis and treatment of varicella. According to Dubey L. et al. (Dubey L. et al., J. Infect. Dis., Vol. 157, pp 882-888, 1988), among leukemia patients to whom a varicella vaccine was administered, those patients suffering from varicella had antibodies to gpI and gpII, but did not have antibodies to gpIII. Among these patients, those patients who recovered were shown to have an increased antibody titer to gpIII.
As seen from the above, it has been attempted to develop HuMAb to gpIII of VZV, which has a high virus-neutralizing activity and a virus spread-inhibiting activity, for prophylaxis and treatment of VZV infectious diseases, but HuMAb to gpIII of VZV has not been obtained.
It is considered that one reason why it is difficult to obtain HuMAb to gpIII in comparison to obtaining HuMAb to gpII is because the amount of antibodies to gpIII produced in a human body is low due to low immunogenicity of gpIII. It is known that when a guinea pig is immunized with an antigen, the production of antibodies to gpIII is low (Keller, P. M. et al., J. Virol. Methods, Vol. 14 pp 177-188, 1986), and that the production of antibodies to gpIII in the human body is also low (Brunell, P. A. et al., J. Infect. Dis., Vol. 156, pp 430-435, 1987).
The above-mentioned low production of antibody in the human body means that the number of lymphocytes which produce antibodies to gpIII is small, and therefore the probability of obtaining a hybridoma which produces HuMAb to the gpIII prepared using those human lymphocytes, is low. This is clear from the experimental results of the present inventors shown in FIG. 2.
Moreover, another reason for the heretofore difficulty in obtaining HuMAb to gpIII is that it is very difficult to detect an antibody to gpIII by ELISA or the like, using disrupted VZV-infected cells as an antigen, as is currently used (Grose et al., J. Infect. Dis. Vol. 157, pp 877-881, 1988). This is also clear from the experimental results of the present inventors shown in FIG. 3B.
Generally, in comparison to gpI and gpII, only a very small amount of gpIII is present in an antigen obtained by disrupting VZV-infected cells, therefore in a screening system using such an antigen, the probability of selecting an antibody to gpIII was very low, and most MAbs selected by such a screening system were antibodies recognizing gpI or gpII (Sugano et al., Eur. J. Immunol., 17, 359-364, 1987).